Over the years, experts have preached the benefits of all sorts of diets, from the cabbage soup to the Atkins to the Mediterranean diets. Back in the 1990s, one of the hottest fads was the zone diet, which called for a precise ratio of carbohydrates, fat and protein at each meal. In the 2000s, actress Gwyneth Paltrow championed the macrobiotic diet, a regimen based upon whole grains and vegetables [source: Rotchford]. Makes you wonder which ones really work.

According to a 2013 article in the Journal of the American Medical Association, there's no scientific evidence that any one of these weight reduction plans is better than the others. An analysis of numerous randomized trials of various diets showed that the differences in their effect on metabolism and body weight was small − the average variation was only 2.2 pounds (1 kilogram) − and inconsistent [source: Pagoto and Appelhans].

However, that doesn't mean that following a diet is necessarily a bad thing. The one consistent effect that the researchers found was that following any sort of reasonable diet and exercise plan would lead to weight loss and improvement in health [source: Pagoto and Appelhans].